In known oil field systems, coiled tubing operations have generally been performed with small diameter tools available for such operations. As coiled tubing is fed into the hole for operations such as drilling, the drilling or other assembly must pass through a relatively large diameter opening at the well head to pass a string of downhole drilling tools that are larger in diameter than the coiled tubing itself. The well head invariably includes a sealing mechanism such as a stripper/packer that can be closed around the coiled tubing as the coiled tubing is being run in and out of the well.
Packers have been in use in oil and gas wells for many years. A packer is generally used in the stack at the well head to seal off down hole pressure from lower well pressures above the packer so that various operations may be performed safely above the well.
A packer commonly comprises a packer element made of a polymeric material that is somehow deformed to seal between a tubular member extending through the packer and the body of the packer. Known well head devices combine the functions of a packer with a BOP, which serves to completely shut off the well when no drill string or coiled tubing is down hole.
Although the packer element is made of a flexible polymeric material, movement of the tubing through the packer abrades the inner surface of the packer, eventually requiring replacement. Sufficient permanent deformation of the packer element will cause the packer to leak by and the packer element must then be replaced. Replacement of the packer element has been shown to be an expensive and often dangerous operation since the packer element is often retained on top by a one-piece bonnet.
In order to replace the packer element, a large number of hold-down bolts, typically 20 or more such bolts, which secure the one-piece bonnet to the body of the packer, must first be removed. Then, the one-piece bonnet must be lifted vertically clear of the packer body, generally two to several feet, to provide clear access to the packer element so that it can be removed and replaced. This vertical clearance above the packer for access to the packer element is otherwise wasted space between the packer and a coiled tubing injector, increasing the overall vertical height of the well-control apparatus at the well head.
Thus, there remains a need for a stripper/packer which provides space saving above the packer and a quick way to change the packer or sealing element, either while tubing is in the well or with the tubing withdrawn from the well.
Further, there remains a need for a stripper/packer/BOP in which the packer element may be replaced quickly and easily without the need for wasted vertical clearance between the packer and any accessory above the packer, such as a coiled tubing injector. This could most advantageously be achieved by horizontally retracting opposed halves of a split bonnet. There also remains a need for a stripper/packer having a split bonnet that resists movement under the influence of downhole pressures when the bonnet is closed.
Such a stripper/packer should be easily adaptable to stacks currently in use, be simple in construction to minimize the cost of construction and enhance the ease of maintenance. Finally, the packer must securely pack off down hole pressure and work at least as effectively as known packers.